Method of bleaching textiles



Patented July 18, 1950 METHOD OF BLEACHING TEXTILES Leslie P. Seyb,.and James L. Foster, Painesville,

Ohio, andHoward l). CIayton Troy, N. Y., assignors to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware Application May 28, 194'79SerialNo. 751,044

6 Claims. (01'. 8l08) This invention relates to bleaching processes for textiles and more particularly for cotton textiles. The invention has as its principal object the provision of a process .for bleaching of cotton gray goods employing hypochlorite, which process compares favorably in results obtained and time consumed and thus in its general economics with all heretofore known processes of bleaching cotton.

Priorart cotton textile bleaching maybe divided into two general processes, those employinghydrogen peroxide or peroxide yielding materials as the main bleaching constituent and those employing compounds releasing available chlorine of which the hypochlorites are wellknown examples.v In recent years continuous peroxide processes have tended to replace hypochlorite processes as the former involved a considerably smaller time from gray goods to finished products than the latter, and thus more material may be processed in a given time and at less expense. Furthermore, peroxide bleaching has been found to lend itself to continuous operation more readily than heretofore proposed embodiments of the hypochlorite method.

The adoption of peroxide methods over hypochlorite methodshas not, however, been entirely a satisfactory solution of the general bleaching problem since peroxide methods, which include kier boiling and-are thus essentially non-continuous, represent n time saving ever. known hypochlorite methods and continuous peroxide methods, considered from the standpoint of bleaching ability, are many times more expensive than hypochlorite. Furthermore, continuous peroxide methods are not equivalent to the older, slower hypochlorite methods when considered from the standpoint of the quality of the bleach.

In view of the tremendous expense involved in tying up large quantities of fabric in prior art hypochlorite processes and also in view of the failure of such processes to compete ona time basis, continuous peroxide processes, though resulting in a less efiicient bleach, are presently preferred in the industry.

Prior to the present invention, there has been a need in the art for a hypochlorite process which materially reduces bleaching time while still yielding bleaching results equal to or better than those obtained by peroxide methods generally and superior to results obtained from continuous peroxide methods. The principal properties involved in comparison of the two bleach methods are whiteness and tensile strength.

The present invention is concerned with a hypochlorite bleaching process which materially reduces the time consumed by previous hypochlorite bleaching processes and results in materials having better properties with respect to whitenessand tensile strength than the commercial ration before caustic steaming or caustic boil- 01?, which step removes'the necessity for subsequent prolonged contact with caustic.

It is-a further object'of the invention to pro- .vide ableaching process which can be accomplished in a relatively short time and which substantially completely removes all motes and other foreign matter in the gray goods while resulting in a material oflsuperior whiteness and superior tensile strength to that obtained by previous bleaching processes.

A further object of the invention is to provide a wetting and penetrating agent in the pretreatment step, whereby not only to increase the speed of the pretreatment step but also to result in an ultimate bleached material of superior whiteness to materials in which the wetting or penetrating agent is not employed.

The single figure of the drawing comprises a flow-sheet of the preferred method of practicing the-present invention against each of which steps are noted the times. involved in the practice of the-steps.

Referring. to the drawing, a sample of cotton .cloth, which has previously preferably been subjected to a singeing treatment to remove loosely held fibers, is padded, dipped, sprayed, or otherwiseflcontacted, l, with a hypochlorite solution, such as sodium hypochlorite, containing available chlorine'of theorder of 4.5 grams per liter or lessand containing about.0.25% of a wetting or penetrating agent materialwhich may be any one of a large number of well-known surface active organic compounds, examples of which are sodium lauryl sulphate, sodium suiphonate of alkylated benzene, Or the like. It will be appreciated that substantially the only limitation upon the choice of the surface active agent, besides its Wetting or penetratingability, is the compatibility of the agent with the pretreatment hypochlorite solution employed. If desired at this step and particularly where the surface active agent chosen tends to incompatibility with hypochlorite. or other chlorinecontaining solutions, thesurface active agent solution may be applied to ,the goods first followed by separate contact with hypochlorite. As this procedure introducesan extra step in the method, a compatible wetting. and penetrating agent and. the combination application of step i of the drawing is pre ferred. The treatment, that is, the length of time which the cloth is actually in contact with this solution, as stated on the drawing, need be no longer than one minute and preferably is shorter than this time, of the order of one-half minute.

Upon completion of the contact step, the cloth is preferably sent to a storage zone, which may be a conventional J-boX, or any suitable means of storage and is held in storage or steeped, 2, for a period up to 60 minutes, though this length of storage is not entirely necessary and a period of about 30 minutes is preferable. Steeping above 60 minutes is not necessarily detrimental to the cloth but is unnecessary in the process of this invention. In the practice of the present invention, it has been found preferable to employ hypochlorite solutions which contain available chlorine of the order of 4.5 grams per liter or less and to employ such hypochlorite in neutral or mildly alkaline solutions, i. e. solutions having a pH of the order of 7.0 to 9.5.

Upon removal from the pretreatment steep, step 2, the goods is washed with water, 3, cold water being preferred in this connection. If desired, an antichlor treatment to be described more fully hereinafter, step l2, may be applied at this point, although such antichlor has in general been found unnecessary for optimum ultimate results. The goods is now sent to a caustic treating step, 4, such as a caustic padder, wherein caustic of the general order of 3% concentration is padded or otherwise worked into the goods. This step occupies about one minute, again taking into consideration the time during which the goods is actually in contact with the caustic solution. Upon completion of the caustic padding step, the material preferably is sent to a steaming zone, 5, where it remains with steam being introduced and passing through the goods for a period of about 20 minutes and upon completion of the 20-minute steaming, is washed, 6, preferably with hot water, again occupying about one minute of time in contact with the hot Water wash.

If desired and in cases where motes and other foreign matter are particularly prevalent in the material being treated, this 20-minute steaming may be repeated after a second padding with caustic soda under conditions corresponding to those used in the first caustic padding. The process of the present invention contemplates the possibility of repeating the caustic treatment, steaming, and washing as many as three times, each steaming period occupying about 20 minutes. If desired, two steaming periods of 30 minutes each, following caustic treatment and followed by washing, may be used or in exceptional cases, a single steaming of 60 minutes, following caustic treatment and including subsequent washing, may be employed. Other variations of time of steaming will occur to those skilled in the art, it being desirable in any event that an efficient final water wash be had.

In the case of employing multiple caustic padding, steaming, and Washing, it has further been found that caustic concentrations below 3% and as low as 0.5% may be used in one or more of the caustic paddings without loss of ultimate whiteness. When such a system is used, it has in general been found preferable to employ the preferred caustic concentration, 1. e. of the order of 3% in the final caustic padding. The preferred practice of the invention, which is applicable in most ordinary cases for bleaching cotton matelonged tie-up of equipment and materials.

rial, however, requires only the one minute contact with 3% caustic soda, followed by 20 minutes in a steam box, after which the caustic treatment need not further be resorted to.

Following the final caustic steamin and hot water wash of the goods issuing therefrom, the goods is treated with a white sour, 1, for which purpose any suitable acid, preferably in a concentration of 1% or less, may be employed and which souring time need not occupy more than one minute. In this connection hydrochloric acid of 1% concentration has been found to be useful. The acid is preferably washed, 8, from the goods in one minute of washing with cold water, following which the goods is contacted with a suitable bleaching solution, 9, preferably containing available chlorine of the order of 4.5 grams per liter or less, such as a hypochlorite solution, for example, sodium hypochlorite. Contact with such hypochlorite, as in the pretreatment, need only occupy a period of about one minute, after which the goods is steeped, In, for a period up to 60 minutes. The period of 60 minutes need not be resorted to in most cases as, in general, it is preferred to leave the goods in the steep for periods of less than 30 minutes, periods of as short as 1'0 minutes having been found satisfactory. Again as pointed out in connection with the pretreatment, continued steeping for longer periods of time does not result in harm to the goods but merely occupies time in the bleaching cycle, which need not be lost and occupies storage space for goods in treatment, which need not be taken up.

At the end of the steeping period, the goods is washed, II, with cold water after which it may suitably be treated, I2, for removal of available chlorine therefrom and for this purpose, any suitable antichlor may be used, such as sodium bisulphite, hydrochloric acid, or hydrogen peroxide. Any of these materials may be used in the concentration of about 1 in accordance with the practices well-understood in the art. For the purpose of the present invention, it has been found that sodium bisulphite in 1% concentration is preferred. Following the antichlor treatment, the goods is preferably washed, [3, again in cold water and is then ready to be dried, l4, dyed, starched, or otherwise finished as is customary in the art.

It will be noted from the general description of the process of the present invention, as set forth above, that prolonged kier boiling may be completely eliminated by the present process and accordingly, a substantial saving in time of treatment and time of equipment use is effected by these means. Thus, it is common practice in ordinary hypochlorite bleaching to kier boil in sodium hydroxide solutions for periods as long as 12 hours. The present invention, which combines the pretreatment with a short caustic boil or alternatively the steaming treatment after caustic padding, completely removes the necessity of prolonged boiling and in particular removes the necessity of such prolonged treatment and pro- In addition, these steps readily adapt themselves to continuous operation, especially in view of the short periods of time involved in the steps of the method.

Gray goods treated in accordance with the present method have usually been previously starched or sized as in the warp threads. In the event of such sizing being present, the usual step of removal of such sizing by enzyme or water treatment priorto the bleach need notbe resorted to in the present invention since in all cases of bleaching of previously sized material, where initial removal of size prior to bleaching has not been had, the quality of thebleach has not varied from that obtained with desized materialand no residual starch is detectable in the finished bleached goods, which indicates that size has been completely removed in the course of the bleaching process.

It-will be appreciated that in general the ultimate tensile strength of material bleached varies tem with kier boiling and broadcloth treated according to a commercial peroxide bleaching system, the comparison being based upon relative whiteness, tensile strength, and heat resistance. In each case the whiteness determinations were made according to the same standard in a Hunter Multipurpose refiectometer, the standard being a magnesium oxide plate having a stated whiteness value of 81.5.

Tensile strength determinations were made with a Scott tester using the grab method according to A. S. T. M. D39--39. The warp breaking strengths were recorded in pounds per inch. The machine was equipped with 3" back jaws and 1" front jaws and operated at a speed of about 12" per minute. The original test pieces measured x 1%" before bleaching and afterwards had shrunk somewhat. However, each test piece was ravelled on one side and then cut in half to give two pieces, each about 5" x 1 The tensile strength was determined on one of these pieces as such, the other piece being set aside for heat resistance determinations to be described. In determining tensile strength, each 5 x 1%" piece of cloth had a 3 inch section marked off as near its center as possible. The jaws of the tester were clamped on the cloth so that 3 inches of cloth were always subjected to the pull of the machine. As nearly as possible, the same threads of the warp were held in the top clamps as in the bottom clamps of the machine. This was-ac complishedv by placing the test sample in the clamps about inch from its ravelled edge.

In determining heat resistance, the other half "of; the test pieces described above comprising '5'{ x 1%" pieces of fabric were heated in a texti'letesting oven for seconds at 400 F. 15 F. Tensile breaks of the type described above are made on this heated piece one hour after heating.

6 It will be seen from Table A above that when broadcloth is treated according to the most rigorous proposed steps of the present method, that is, with three successive treatments of caustic, each followed by three 20-minute steamings, the

tensile strength of the resulting bleached fabric is substantially better than that of prior art treated materials and whiteness is also improved. The improvement over the results obtained by known hypochlorite bleaching methods, which includes lengthy kier boiling, is especially notable.

It will be appreciated that where sodium hypochlorite is referred to, othercompositions able to produce available chlorine may be included. In general, alkali metal and alkaline earth metal hypochlorites may be used in the present invention, it being obvious that sodium hypochlorite is the most satisfactory for general purposes in view of its easy availability.

As noted above, the addition of wetting agent in the pretreatment step has the effect not only of increasing the speed with which this step may be completed but also has a desirable effect upon the whiteness of ultimately bleached material. It has been found that not only is the wetting agent a means of considerably reducing the time necessary for contact with the pretreatment hypochlorite but also thatwhiteness is considerably improved over the same method of bleaching not using the wetting agent in this step.

As stated above, the pH range found preferable for the method of the present invention is between pI-I 7.0 and 9.5. More particularly and with reference to the lower end of this pI-I range, it is in general preferred when operating closer to neutrality to employ a relatively low concentration of available chlorine of the order of 1.5 g. p. l. or below and to employ pretreatment and bleaching steep times in the lower end of their operable range, such as 30 minutes or less. When the pH approaches the upper limit, however, substantially no difference in whiteness or tensile strength is observed at different concentrations of available chlorine or times of steeping heretofore described. Within the definitions set forth above, the pH range of 7.0 to 9.5 is especially desirable as there exists within this range a natural buffer set up between undissociated hypochlorous acid and hypochlorite ion, which simplifies the maintaining of the desired pH.

In addition, it has been found that in general the concentration of available chlorine does not modify the whiteness obtained when the avail.- able chlorine is present from about 0.30 to about 3.0 grams per liter. In general, chlorine concentration below 0.30 gram per liter is found not to effect the bleaching with sufficient speed to justify its use; some improvement in whiteness, where chlorine in an amount of above 3 grams per liter is present, is noted but a higher concentrations tensile strength of the ultimate material is modifled in an unfavorable manner so that at about 4.5 grams per liter, the loss in tensile strength begins to exceed that justified for the purpose of obtaining superior whiteness. Accordingly, a concentration of available chlorine of the order of 3 grams per liter is in general preferred as providing the optimum balance between improved whiteness and decreasing tensile strength.

As noted above, under normal conditions, the entire bleaching process from gray goods to finished bleached goods may be accomplished in a period of two hours under ordinary circumstances and in no event, even in the case of the mostdifficult bleaching problem, will more than three-hours be occupied in treatment of cotton goods. The various solutions described as padded or otherwise introduced into the material may be applied to the materials in any desired manner, such as soaking, submerging, and the like, though padding as will be understood by those skilled in the art is in general preferred. Furthermore, though soaking for periods'of time described as steeping times may be resorted to, in' general, it is preferred to steep the solution treated material out of actual submergence in such solution.

In general (and with the exception of the described steamings and preferred hot water washes), it has been found satisfactory to operate the method of the present invention at room temperature, that is, at-a temperature of the order of 25 C. This is especially true since no particular advantage has been found in operat ing at a temperature above this range, especially since at relatively high temperatures, a noticeable loss of tensile strength is observed even though a slight gain in whiteness may also be had. With respect to whiteness, it has also been observed that materials treated in accordance with the method of this invention show negligible loss of whiteness in storage periods up .to as long as six months and more.

It has, in general, been found preferable to opcrate the entire bleaching process at atmospheric pressure though, if desired, increased pressures may be used for steaming, no appreciable gain having been observed therefrom. Those skilled in the art will understand that where treatment with caustic soda is described, the hydroxides of other alkali metals may also be used in equivalent concentration. However, from the standpoint of convenience and general availability, it is obviously preferable to employ sodium hydroxide in this connection. Similarly, it will be appreciated that various kier assistants, such as sodium silicate, pine oil, soaps, or other detergent materials, may be employed with the caustic or other hydroxide treatment.

The present invention may be practiced prior to or after mercerization or, if desired, mercerization may be had in the course of the bleaching process of this method at any convenient point, depending upon operation of the bleach plant.

It will be appreciated that the apparatus used for the practice of the present method is not a critical part of the present invention. On the contrary, any convenient apparatus may be used, this consideration being somewhat controlled by the desire of the operator to conduct the method on a batch, semi-continuous, or totally continuous basis. It may be pointed out that the method is particularly adapted for totally continuous operation, especially since the steeping and holding times are relatively short so that expensive equipment, such as J-boxes and other equipment designed for steeping of textiles in bleaching proc- -esses, need not be tied up unduly. The method of the invention, however, will operateequally well when working on a strictly batch basis and moving the materials by hand or by conveyor, if desired, from one zone of treatment to another.

In order more fully to inform those skilled in the art of the preferred practice of the present invention, the following examples are offered of preferred procedures which have been found to be particularly effective in the bleaching of gray goods. No limitation of the present invention is to be implied from these examples, the same being ofiered rather as illustrative of the preferred practice of the invention. In the examples where times of treatment are described, times of actual contact with the goods are meant.

Example I agent-sodium hypochlorite aqueous system con taining 250 lbs. of 3 grams per liter aqueous so'- dium hypochlorite of pH 9.0 and 0.625 1b. of wet ting agent comprising sulphated higher fatty acid alcohol. The concentration of wetting agent amounts to 0.25% in the solution. The contact time of the gray goods with the wetting agent sodium hypochlorite solution is A; minute. The goods is sent to a steeping chamber comprising a J-box, which is operated at room temperature, and held there for 30 minutes, after which the goods is washed with cold water to removed es sentially all of the sodium hypochlorite-wetting agent solution. From here the goods is sent'to a caustic soda padder, again operated at rooni temperature, where it is held in contact fora time of A minute with a solution comprising 150 lbs. of water and 100 lbs. of 7.5% aqueous caustic soda, amounting in all to caustic soda of a'con centration of 3%. The goods is now sent to a steaming chamber operated at atmospheric pressure for a contact time of 20 minutes, after which it is washed in hot water between and C. to remove gelatinous or other undesirable bodies from the fabric, the wash occupying minute. As has been pointed out above, the steps of caustic soda padding, steaming, and hot water washing may be repeated if desired but in the material of this example, such repetition is unnecessary. The material is now sent to a white sour padder wherein 1% HCl of an amount of lbs. is contacted with the goods for a period of minute, after which a cold water wash for a period of /2 minute is employed, followed by a sodium hypochlorite padding for V4 minute. The second sodium hypochlorite treatment comprises contacting the 1,000 yards of goods with 100 lbs. of pH 9 sodium hypochlorite containing '7 .5 grams per liter available chlorine and lbs. of water, which amounts to overall available chlorine of 3 grams per liter. The material is now sent to a steeping chamber, such as a J-box, which is op;- erated at room temperature and held there for 30 minutes, and then to a cold water wash wherein the sodium hypochlorite solution is washed out with Water. The material is now padded with a mixture of 150 pounds of water and 100 pounds of 1% aqueous sodium bisulphite, the contact time of the goods with the sodium bisulphite solution being A minute. This is followed by cold water washing for /g minute, whereupon the material may be dried. The goods is found to be bleached to a whiteness in excess of that obtained by kier boil sodium hypochlorite treatment or by kier boil hydrogen peroxide treatment. "I'he tensile strength of the material is considerably in excess of either the commercial hypochlorite type or the peroxide type bleached material.

In contrast to Example I, the material treated in the following example is an extremely crude,

rough type of cotton material representing perhaps the extreme from the highly refined broadcloth treated in Example I.

Example II A coarse, loosely-woven, gray goods having a count of 44 x 46 threads per linear inch and being a material generally used for makingfiour sacks and containing a large amount ofmotes and other foreign matter, is padded at room temperature with a wetting agent-sodium hypochlorite solution containing 0.25% wetting agent and 3 grams per liter available chlorine and having a pH of 9.0 for minute, after which the material is sent to a steeping chamber for a :period of 30 minutes. A cold water wash removes the grossly held hypochlorite, after which the material is sent to a caustic soda padder for a contact of A; minute, the caustic soda havin a concentration of 3% after making allowance for incoming water held by the goods. The material is then sent to a steaming chamber for a period of 20 minutes at atmospheric; pressure and is hot water washed at 75-95 C. following the steaming. The steps of caustic soda contact, steaming, and hot water washing are repeated twice more, after which the material is padded with 1% HCl for a contact time of A; minute and cold water washed for a contact time of minute, and then sent to a sodium hypochlorite padder for /i.minute, wherein the sodium hypochlorite concentration of chlorine is 3 grams per :liter, again allowing for incoming water, the solution having a pH of 9.0. The material is now steeped for a periodof 30 minutes and then is washed in cold water for a period of /2 minute .to remove essentially all ofthe sodium hypochlorite solution. An antichlor of 1% sodium bisulphite is now contacted with the material for a period of A; minute and the material is cold .water washed for a period of minute,after which it isdried. This material is found to be substantially free of motes and other foreign matter and to have a whiteness far in excess of any whiteness obtainable on similar material by any other known bleaching processes, as well as a tensile strength equal to orbetter than the tensile strength of similar materials bleached by prior art processes.

Example III 1 Material of the type treated in- Exa-mple I is submersed in a solution having a pHof 7.0 and containing 0.25% wetting agentiand sodium hypochlorite suflicient to make available 0.65 gram per liter of chlorine. The goods is held submerged in the solution at room temperature for a period of ten minutes. Upon removal from the pretreatment solution, the goods is cold water washed and sent to a caustic padder, where it is padded with 3% caustic soda solution, steamed for 20 minutes and hot water washed. The padding, steaming for 20 minutes, and washing are repeated twice more. The goods is now soured with 1% hydrochloric acid and after cold water wash is submerged for a period of minutes in a sodium hypochlorite solution having 1.49 grams per liter of available chlorine and a pH of 7.0. Upon removal from the bleach solution, the goods is washed, antichlored, and washed as in Example I. The finished goods is superior to commercial hypochlorite bleached materials, both.

as to whiteness and tensile strength, and compares favorably in these respects to commercial peroxide bleached goods.

As pointed out hereinbefore, it is sometimes desirable where the caustic contact, steaming, and wash are repeated to reduce the concentra tion of causticin one or more of the repeated contacts both because equivalent whiteness may be obtained by this method and to eflect a savingin caustic. Exam le, IV is an illustration of the manner in which the invention may be practiced according to this modification.

Example IV Material of the type treated in Example II is padded at room temperature with a wetting agent-sodium hypochlorite solution containing 0.25% wetting agent and initially 3.12 grams per liter of available chlorine and having a pH of 9.0 for minute, after which the material is sent to a steeping chamber for a period of 30 minutes. A cold water wash removes the grossly held hypochlorite, after which the material is sent to a caustic soda padder for a contact of minute,

the caustic soda having a concentration of 0.5% after making allowance for incoming water held by the goods as introduced. The material is then sentto a steaming chamber for a period of 20 minutes, which steaming is conducted at atmospheric pressure. Following the steaming, the goods is hot water washed at 75 to C. The goods is now recontacted with a caustic soda solution in the same manner as before, the solution having'a concentration in this second contact of 3% in caustic soda. The steamin treatment is now repeated for a :period of 20 minutes and-is followed by hot water wash as before. The material is now padded with 1% hydrochloric acid for a contact time of A; minute and is further contacted with a cold Water wash for a contact time of minute and is then sent to a sodium hypochlorite padder for A; minute, wherein the concentration of available chlorine initially is 3.12 grams per liter and the pH is 9.0. The goods is now steeped for a period of 30 minutes and is then washed in cold water for a period of /2 min-'- ute to remove essentially all of the sodium hypochlorite solution held thereon. Antichlor of 1% sodium bisulphite is now contacted with the goods for a period of A; minute and the material is cold water washed for a period of /2 minute, after which ,it is dried. Upon examination, the material is found to have a whiteness comparable to the whiteness obtained by the method of treating disclosed in Example II and furtheris found to have a whiteness in excess of any whiteness obtainable: by commercial methods upon similar type goods.

While we have described in detail certain forms of our invention and certain specific examples of its practice, we do not wish to be understood as limiting ourselves to the use of such examples as we realize that changes within the scope of the invention are possible, and we further intend each step in the following claims to refer to all equivalent steps for accomplishing the same result in substantially the same or equivalent manner, it being our purpose to cover our invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. The continuous process of bleaching cotton materials which includes the steps of contacting cotton gray goods with a hypochlorite solution.

having an available chlorine concentration maintained substantially constantly between 0.3 and 4.5 grams per liter and having a pH maintained substantially constantly between 7.0 and 9.5 and containing a wetting and penetrating agent, steeping said goods in contact with said hypochlorite solution, removing said goods from steeping, and contacting said goods with a caustic solution solution, the time of contact with any solution being of the order of up to one minute and the time of steeping at any steeping step being of the order of up to 60 minutes.

2. The method as' claimed in claim 1 wherein the pH is maintained within the range of 7 .0 and 9.5 in the presence of a buffer between undissociated hypochlorous acid and hypochlorite ion.

3. The continuous process of bleaching cotton materials which includes the steps of providing a series of goods contacting solutions and holding zones in the order given as follows: A hypochlorite solution having a pH maintained substantially constantly between 7.0 and 9.5 and having an available chlorine concentration maintained substantially constantly between 0.3 and 4.5 grams per liter, and containing a wetting and penetrating agent, a holding zone, a water wash, a caustic solution containing of the order of between 0.5% and 3% caustic, a holding zone, a water wash, a white sour solution comprising dilute acid, a water wash, a second hypochlorite solution having a pH maintained substantially constantly between 7.0 and 9.5, and having an available chlorine concentration maintained substantially constantly between 03 and 4.5 grams per liter, a holding zone, a water wash, an antichlor solution, and a water wash, continuously passing cotton gray goods through said zones and solutions, the time of contact with any solution being of the order of up to one minute, and the time of holding in any holding zone being of the order of up to 60 minutes.

4. The method as claimed in claim 3 which includes the steps of providing a bufier comprising hypochlorous acid, hypochlorite ion in said available chlorine solution.

5. The method as claimed in claim 3 which includes a separate wetting and penetrating agent solution and. a separate first hypochlorite solution and continuously passing said oods first through said wetting and penetrating agent solution and then through said hypochlorite solution.

6. The method of bleaching cotton cloth which includes the steps of contacting cotton gray goods with a hypochlorite solution having an available chlorine concentration maintained substantially constantly between 0.3 and 4.5 grams per liter of available chlorine, and having a pH maintained substantially constantly between 7.0 and 9.5 and containing a Wetting and penetrating agent, removing said goods from contact with said solution, steeping said goods, contacting said goods with a caustic solution containing about 0.5% caustic soda for a period of less than one hour, water washing said goods, recontacting said goods with a caustic solution containing about 3% caustic soda for a period of less than one hour, water washing said goods, contacting said goods with a weak acid solution, contacting said goods with a second hypochlorite solution having a pH maintained substantially constantly between 7.0 and 9.5, and having an available chlorine concentration maintained substantially constantly between 0.3 and 4.5 grams per liter of available chlorine, and steeping for a period of less than one hour.

LESLIE P. SEYB. JAMES L. FOSTER. HOWARD D. CLAYTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 333,875 Mather Jan. 5, 1886 396,551 Drown Jan. 22, 1889 635,248 I-Iadfield Oct. 17, 1899 1,061,392 Mathesium May 13, 1913 1,146,461 Taylor July 13, 1915 1,630,786 Conrad May 31, 1927 2,202,332 Butterworth May 28, 1940 2,236,617 Brandt Apr. 1, 1941 2,267,718 Campbell Dec. 30, 1941 FOREIGN PATENTS Number Country Date 399,320 Great Britain Oct. 5, 1933 OTHER REFERENCES Boyd, Cotton Piece-Goods Bleaching. Melliand Textile Monthly, Sept. 1931, pp. 493-495; Oct. 1931, pp. 530-583. 

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